SU896341A1 - Rectification process automatic control method - Google Patents

Description

(54) AUTOMATIC CONTROL METHOD FOR RECTIFICATION PROCESS

one

This invention relates to the automation of industrial processes and can be used in the production of oxygen from atmofer air.

There is a method for automatically regulating the process of rectification by changing the flow rate of the expander flow depending on the level of the product in the lower column and the reflux rate of the upper column depending on the level of the product in it 1.

The closest to the technical essence of the invention is a method of automatic regulation of the distillation process, which consists in the fact that when controlling the flow of production oxygen, a correction is made in terms of air flow and oxygen concentration on the intermediate plate of the upper distillation column, and the reflux flow rate of the upper distillation column changes in depending on the oxygen concentration in the irrigation flow 2.

However, the known method of automatic regulation only improves the quality of the stabilization of production oxygen, but also, like the first, does not allow

minimize the loss of oxygen with nitrogen when changing the load or cold loss of the air separation unit.

The purpose of the invention is to minimize the loss of oxygen with nitrogen and to increase the capacity of the air separation unit.

This goal is achieved by changing the flow rate of production oxygen and the flow rate of irrigation of the upper distillation column with appropriate proportionality coefficients depending on the pressure change in the lower distillation column and the flow rate of the expander flow from the lower distillation column to the upper distillation column. Changes in the costs of production oxygen 15 and irrigation of the upper distillation column measure the concentration of production oxygen and the oxygen content in the nitrogen at the outlet of the upper distillation column and when the deviation of the production oxygen concentration deviates from

20 of a given value or concentration of oxygen in nitrogen at the outlet of the upper distillation column from the minimum possible value changes the indicated coefficients of proportionality, and the value of the minimum possible oxygen value in nitrogen is determined by the suppression in the lower distillation column and the flow of the expander flow.

The drawing shows a block diagram of an automatic control system implementing the described method.

The initial mixture (air) is fed to the lower distillation column 1, where it is separated into nitrogen and oxygen-enriched air (bottom liquid), which as the initial mixture is fed to the separation into the upper distillation column 2. By a reflux condenser of the lower distillation column 1 and simultaneously with a boiler The upper distillation column 2 is the condenser-evaporator 3. The distillate of the lower distillation column 1 is taken from the pockets located in its upper part, and through the sub-cooler 4 is sent to the irrigation tank the upper distillation column 2. To compensate for the cold loss of the installation, a portion of the air (the expander flow) is taken from the lower distillation column 1, expanded in the expander 5 and at a temperature close to the saturation state, as the initial mixture is fed to the separation in the upper distillation column 2 From the bottom of the upper distillation column 2, production oxygen is taken, and nitrogen is taken from above.

The system of automatic control of the distillation process consists of a computational% Ac1 6, which inputs signals from flow rate sensors 7, a pressure sensor 8 in the lower distillation column 1, a sensor 9 for oxygen concentration in nitrogen at the outlet of the distillation column 2, and a production concentration sensor 10. oxygen. The control actions from the computational mask 6 are fed to the setters of the controller 11 for the flow of production oxygen and the controller 12 for the irrigation of the upper distillation column 2.

The method of automatically controlling the air rectification process is carried out as follows.

Signals from the expander flow sensor 7 and pressure sensor 8 in the lower distillation column 1 are inputted to the computer 6 at a given frequency. After each survey, the current values of these parameters are compared with their values obtained during the previous survey cycle. When changing the flow rate of the expander flow or pressure in the lower distillation column 1 by an amount greater than the specified, the newly obtained values of these parameters determine the new flow rate of the production cell and the irrigation flow rate of the upper distillation column 2.

The calculation of the consumption of production oxygen and irrigation of the upper distillation column 2 is made according to the expressions

G K. OD + K, p + K, U,

(i;

iR

 . .- - KeUz - (2)

GO + Kjp

where, is the consumption of production oxygen;

G (j is the flow rate of the upper distillation column 2; Std is the flow of the expander flow; P is the pressure in the lower distillation column 1;

Y, .n is a predetermined concentration of production oxygen; K, -Kg-constant coefficients.

The values of constant coefficients K, -Kb are found according to a mathematical model of the process from the condition of minimum loss of oxygen with nitrogen, as a result of which the consumption of production oxygen calculated by expression (1) is the maximum possible for the given conditions of operation of the air separation unit.

After each change of the setpoint signals to the controller 11 for the flow of production oxygen and the controller 12 for the irrigation of the upper distillation column 2 from the computational mask 6, after the transition process, the oxygen concentration in nitrogen is interrogated at the 0 output from the upper distillation column 2 at the air separation unit and a production oxygen concentration sensor 10.

The value of the concentration of oxygen in nitrogen at the exit of the upper distillation column 2 is compared in computational mask 6 with the previously found optimal value, and the value of concentration and production oxygen is compared with a given concentration of production oxygen. If the absolute value of the difference of the compared parameters exceeds a predetermined value, then the proportionality coefficients K-Kb Dependencies (1) and (2) used in computer 6 for determining the consumption of production of oxygen and irrigation of the upper distillation column 2 are changed.

Unlike the known methods of automatic control of the air separation process, the purpose of which is reduced exclusively to stabilization of the process mode, the proposed method allows finding the best mode of the rectification process, providing for any current conditions the maximum possible air separation plant capacity. The implementation of this method allows to increase the capacity of the air separation unit by 3-4%, at constant costs for the production of oxygen.

Claims (1)

Claim A method for automatically controlling the process of air distillation, carried out in the upper and lower distillation columns, by regulating the flow of oxygen ₅ and the irrigation flow of the upper distillation column, characterized in that, in order to minimize the loss of oxygen with nitrogen and increase the productivity of the air separation unit, the production oxygen flow rate and the irrigation flow rate of the upper distillation column are changed with the corresponding proportionality coefficients depending on changes in pressure in the lower distillation column and the flow rate of the expander stream coming from the lower distillation column ¹⁵ to the upper distillation column, and after each change in the production oxygen consumption and irrigation of the upper distillation column, the concentration of production oxygen and the oxygen content in nitrogen at the outlet the upper distillation column and when the deviation of the concentration of production oxygen from a predetermined value or the concentration of oxygen in nitrogen is exceeded by Exit from the top of the distillation column from the minimum possible value of said change proportionality coefficients and the magnitude of minimum possible values of oxygen in nitrogen is determined by the pressure at the bottom of the distillation column and the flow rate of expander flow.